Update scarb new/init hello world Cairo code

examples/hello_world/src/lib.cairo

@@ -1,19 +1,17 @@
-fn main() -> felt252 {
+fn main() -> u32 {
     fib(16)
 }
 
-fn fib(mut n: felt252) -> felt252 {
-    let mut a: felt252 = 0;
-    let mut b: felt252 = 1;
-    loop {
-        if n == 0 {
-            break a;
-        }
+fn fib(mut n: u32) -> u32 {
+    let mut a: u32 = 0;
+    let mut b: u32 = 1;
+    while n != 0 {
         n = n - 1;
         let temp = b;
         b = a + b;
         a = temp;
-    }
+    };
+    a
 }
 
 #[cfg(test)]

extensions/scarb-cairo-run/tests/examples.rs

@@ -97,7 +97,7 @@ fn can_limit_gas() {
                 Finished release target(s) in [..]
                  Running hello_world
             Run completed successfully, returning [987]
-            Remaining gas: 68340
+            Remaining gas: 50760
         "#});
 }
 

scarb/src/ops/new.rs

@@ -156,22 +156,20 @@ fn mk(
         fsx::write(
             source_path,
             indoc! {r#"
-                fn main() -> felt252 {
+                fn main() -> u32 {
                     fib(16)
                 }
 
-                fn fib(mut n: felt252) -> felt252 {
-                    let mut a: felt252 = 0;
-                    let mut b: felt252 = 1;
-                    loop {
-                        if n == 0 {
-                            break a;
-                        }
+                fn fib(mut n: u32) -> u32 {
+                    let mut a: u32 = 0;
+                    let mut b: u32 = 1;
+                    while n != 0 {
                         n = n - 1;
                         let temp = b;
                         b = a + b;
                         a = temp;
-                    }
+                    };
+                    a
                 }
 
                 #[cfg(test)]